Aerobic biological treatment of a pharmaceutical wastewater: Effect of temperature on COD removal and bacterial community development

The effect of temperature was studied on the efficiency of soluble COD removal and bacterial community development during the aerobic biological treatment of a pharmaceutical wastewater. Using wastewater and bacterial inoculum obtained from the full-scale facility treating this wastewater, batch laboratory cultures were operated at 5°C intervals from 30°C to 70°C. Following four culture transfers to allow for bacterial acclimation, residual soluble COD levels were measured and bacterial community fingerprints were obtained by denaturing gradient gel electrophoresis (DGGE) of polymerase chain reaction (PCR)-amplified 16S rRNA gene fragments. Soluble COD removal efficiency declined as temperature increased from 30°C (62%) to 60°C (38%). Biological treatment of this wastewater failed to occur at temperatures higher than 60°C. Gradual shifts in bacterial community structure were detected as temperature increased, including a concomitant reduction in the number of different bacterial populations. The impact of temperature on a two-stage biological treatment process was also compared. Better soluble COD removal was achieved when both reactors were operated at 30°C compared to a system where the two stages were consecutively operated at 55°C and 30°C. These results indicate that operation of aerobic biological wastewater treatment reactors at elevated temperatures can have adverse effects on process performance.